This application relates to a controlled release fertilizer, i.e., a material which releases its fertilizer component for utilization to the soil over a sustained and rather prolonged period of time.
Fertilizers of course, have been used for many years to improve the quality of soil, and particularly for application to the soil for the purpose of providing various nutrient, growth sitmulant and other positive factors to seeds and plants to enhance their growth and production.
It is well known that solid fertilizers tend to be rapidly absorbed and degraded in the soil. This rapid absorption and degradation limits the longevity of the fertilizer's usefulness causing low efficiency of plant utilization when compared to the nutrients initially available, and increasing production costs by requiring frequent reapplication. Various chemical and/or mechanical inhibitors or retardants have therefore been employed to decrease these rapid absorption and degradation rates. The objectives sought to be achieved by utilizing such inhibitors or retarders is to release assimilable amounts of certain nutrients, stimulators and the like over a relatively long period of time.
Various approaches have been made in the past to provide a solid fertilizer material which utilizes these mechanical or chemical inhibiting or retarding means, such as a coating, to cause the fertilizer to be released to the soil and surrounding plant life over a relatively long period of time. Some of these methods have been relatively successful. For example, fertilizers in small pellet or bead form have been coated with various polymer-like materials. Some polymer coatings have been effective to control the release of the encapsulated fertilizer in such a way that it becomes available to the soil and plant life therein over a period of many days or weeks, as contrasted to an almost immediate total release. However, when such polymers are used as the sole coating material, large amounts are required to attain the desirable release characteristics. A marked disadvantage of a control release fertilizer utilizing such polymer coatings is the high cost of the polymer used. This naturally makes the ultimate product expensive. Moreover, when the polymers are utilized as the exclusive coating agent, difficulty in obtaining a desired release rate has been experienced.
Additionally, micronutrient trace elements such as, for example, boron and manganese, are known to be required for proper growth of all plants. These micronutrient trace elements, however, need only be present in minute amounts to be effective. Moreover, such micronutrient trace elements should preferably be released to the soil and plants herein at a more rapid rate than other fertilizer material such as the macronutrients consisting of nitrogen, phosphorous and the like.
When single coating techniques, such as coating with various polymer-like materials is used, all nutrients, including any micronutrient trace elements contained within the encapsulated material are caused to be controllably released. Thus, a control release fertilizer containing only a single coating cannot selectively release different fertilizing constituents at differing intervals.